1. Field of the Invention
The present invention relates to a doctor blade assembly, and more specifically relates to an upper seal for a doctor blade assembly which inhibits toner leakage generally in the area of the developer housing and the doctor blade bracket assembly.
2. Description of the Related Art
Laser printers utilize a light beam which is focused to expose a discrete portion of a photoreceptive or image transfer drum in a further attempt to attract printing toner to these discrete portions. One component of a laser printer is the photoreceptive drum assembly. This photoreceptive drum assembly is made out of highly photoconductive material that is discharged by light photons typically embodied by a laser. Initially, the drum is given a charge by a charge roller. As the photoreceptive drum revolves, the printer shines a laser beam across the surface to discharge certain points. In this way, the laser “draws” the letters and images to be printed as a pattern of electrical charges—an electrostatic latent image. The system can also work with either a more positively charged electrostatic latent image on more negatively charged background or a more negative charged electrostatic latent image on a more positively charge background.
The printer's laser or laser scanning assembly draws the image to be printed on the photoreceptive drum. The traditional laser scanning assembly may include a laser, a movable mirror and a lens. The laser receives the image data defined by pixels that make up the text and images one horizontal line at a time. As the beam moves across the drum, the laser emits a pulse of light for every pixel to be printed. Typically, the laser doesn't actually move the beam. Instead, the laser reflects the light beam off of a movable mirror. As the mirror moves, the light beam passes through a series of lenses. This system compensates for the image distortion caused by the varying distance between the mirror and points along the drum. The laser assembly moves in one plane horizontally as the photoreceptor drum continuously rotates so the laser assembly can draw the next line. A print controller synchronizes this activity. The process of forming the light image on the photoreceptive drum discharges those areas where the image is formed.
When the toner becomes electrostatically charged, the toner is attracted to exposed portions of the image transfer drum. After the data image pattern is set, charged toner is supplied to the photoconductive drum. Because of the charge differential, the toner is attracted to and clings to the discharged areas of the drum, but not to the similarly charged “background” portions of the photoconductive drum. Toner is an electrostatically charged powder with two main ingredients, pigment and plastic. The pigment provides the coloring, such as black in a monochrome printer to form text and images. This pigment is blended with plastic particles, so the toner will melt when passing through the heat of a fuser assembly. The toner is stored in the toner cartridge housing, a small container built into a removable casing. The printer gathers the toner from a sump within the housing and supplies it to a developer unit using paddles and transfer rollers. The developer roll is a charged rotating roller, typically with a conductive metal shaft and an polymeric conductive coating, which receives toner from a toner adder roll position adjacent the developer roll. Due to electrical charge and mechanical scrubbing, the developer roll collects toner particles from the toner adder roll. A doctor blade assembly engages the developer roll to provide a consistent coating of toner along the length and surface of developer roll, by scraping or “doctoring” excess toner from the developer roll. The doctor blade may also induce a charge on the toner. In turn, this provides a consistent supply of toner to the photoconductive drum. When the coating of toner on the developer roll is inconsistent, too thick, too thin or bare, coating of the photoconductive drum is inconsistent and the level of darkness of the printed image may vary unintentionally, which is considered a print defect.
The electrostatic image on the photoconductive drum is charged such that the toner particles move from the developer roll onto the latent image on photoconductive drum. With the image data toner pattern on the photoconductive drum, the drum engages a sheet of paper or media moving adjacent thereto. The paper or other media is driven by a transport belt, which is oppositely charged to the toner causing it to transfer to the paper or other media. This charge is stronger than the charge of the electrostatic image, so the paper can pull the toner powder away from the surface of the photoconductive drum. When a medium, printing paper, passes beneath the rotating photoconductive drum, the toner is transferred to the medium. Since it is moving at the same speed as the drum, the paper picks up the image pattern exactly. To keep the paper from clinging to the drum, it can be discharged immediately after picking up the toner.
One problem with existing doctor blade assemblies is that of providing a consistent seal generally around the location where doctor blade assembly and the developer housing meet due to the tolerances and stiffness of the seal utilized in this location. Additionally, as shown in the prior art device depicted in FIG. 7, the corner area where the bracket and doctor blade meet also provides a leakage path. The paddles that move the toner from the sump to the developing components of the cartridge cause a cyclical internal toner pressure in the cartridge. The operational toner pressure as well as vibration and drop testing has demonstrated this corner location to be a frequent toner leak path, especially in higher volume developer housings. The leakage occurs in the area of the blade and bracket corner due to deformation of the upper portion of the j-seal when the bracket assembly is disposed thereon.
It would be desirable to inhibit toner leakage in the area of the corner of the developer housing as well as the corner where the bracket and blade meet without adding additional parts or increasing expense through additional components to seal this area.